An irregular microscopic network of vascular canals, containing yellow matter, is seen in the soft substance which covers the sail; it ends in a canal round its margin. A similar system exists both in the upper and under-surface of the disk. All these systems are connected with one another, and with organs pending from the inferior side of the disk, which are hid when the Velella is in its natural horizontal position. These organs consist of a large central sterile polypite, which supplies the whole system with elaborated juices; it is surrounded by smaller polypites, which are both nutritive and reproductive; and the whole is encircled with a ring of prehensile and armed tentacles fastened to the rim of the disk, immediately adjoining to the under-side of the limb. The pneumatic filaments already mentioned are mixed with these different organs. In the Velellidæ caught by M. Vogt, he invariably found the stomachs of the large as well as of the small polypites, full of the carapaces of minute crustacea, shells, the bones of small fishes, and larvæ, so as even to be swelled out with them. The indigestible parts are thrown out at the mouth, and the elaborated juices are transferred to the various systems of canals to be distributed through all the members of the animal. The mouths of the small polypites take various forms; sometimes they are wide and trumpet-shaped, with everted lips, sometimes they are contracted. These small polypites consist of a double sac, fastened to the disk by a hollow stem with many rounded elevations on their surface full of thread-cells. The tentacles of the Velellidæ are strong, thick, club-shaped tubes, completely closed at their extremities, which abound in thread-cells; their cavity is filled with a transparent liquid, supposed to play an important part in their elongation. Medusiform zooids are formed on the slender stems of the small polypites. It is presumed that they lay fertilized eggs which yield Velellidæ, so that this animal has probably alternate states of existence; but nothing is known of its earliest stages of development. The youngest form yet discovered is that described by Prof. Huxley, in his excellent monograph on ‘Oceanic Hydrozoa.’[26] The Velellidæ are inhabitants of warm and tropical seas, but are occasionally found on the coasts of Great Britain, being carried by the Gulf Stream to the Bay of Biscay, and thence wafted northwards by the prevalent winds.